1. Field
The present application relates to gas turbines, and more particularly to an arrangement to prevent thermocouple chafing with a guide tube within a rotor disc cavity, as well as a method to prevent premature gas turbine shutdown due to rotor disc cavity thermocouple failure.
2. Description of the Related Art
Thermocouples are used within the turbine section of a gas turbine engine to give an indication of the condition of the rotor disc cavity. The rotor disc of the turbine section is a critical component of the gas turbine which is exposed during engine operation to high centrifugal stresses and high temperatures. Thus, it is crucial to have a continuous indication of the rotor disc. A temperature sensing element of a thermocouple can give such an indication.
Routinely, thermocouples are inserted into the gas turbine through guide tubes positioned within radial extending bores in components of the turbine section of the gas turbine. Ideally, this series of guide tubes are connected with each other in a straight line configuration. The components through which the guide tubes are positioned may include the outer casing, the turbine blade ring, a turbine vane, and the interstage seal housing such that when fully inserted, the tip portion of the thermocouple which includes the temperature sensing element is positioned within the rotor disc cavity. The rotor disc cavity is situated between two adjacent rotor discs.
Two thermocouples are used per stage of turbine vanes so that a redundant system exists; i.e., if one thermocouple is damaged and is non-operational, a second thermocouple may be operational and relied upon for the temperature reading of the rotor disc cavity of that stage. Such a redundant system may prevent premature gas turbine shutdown. However, occasionally, both thermocouples fail resulting in a premature gas turbine shutdown.